1. Field of the Invention:
The present invention relates to a compression bonded type semiconductor device, such as GCT (Gate Commutated Turn-off) thyristor.
2. Description of the Background
Although a GTO (Gate Turn-OFF) thyristor has been widely used as a device for large capacity power electronics, the GTO requires a snubber circuit. Further, it is difficult to suppress an increase of snubber loss due to an increase in an operating voltage of the GTO. However, a GCT (Gate Commutated Turn-off) thyristor does not require such a snubber circuit and realizes a performance of 6000 A for a maximum breaking current and less than or equal to 3 xcexcs for a turn-off storage time. The GCT also has an increased capacity and speed.
FIG. 3 is a cross-sectional view illustrating a background compression bonded type semiconductor device (e.g., a GCT) described in Japanese Patent Laid-Open No. Hei. 8-330572 (1996). In the figure, reference numeral 1 denotes a semiconductor substrate. An aluminum gate electrode 2a is formed at an outer peripheral portion on a surface of the semiconductor substrate 2, a cathode electrode 2b is formed at an inside of the gate electrode 2a, and an anode electrode 2c is formed on a back surface of the substrate 2. Also shown are a cathode distortion buffer disk 3 and an external cathode electrode 4 mounted one after another on a side of the cathode electrode 2b, and an anode distortion buffer disk 5 and an external anode electrode 6 mounted one after another on a side of the anode electrode 2c. A ring gate electrode 7 made of iron or nickel alloy contacts the gate electrode 2a, and a ring-shaped external gate terminal 8 made of iron or nickel alloy is electrically connected with the ring gate electrode 7, though it is not fixed thereto. In addition, an elastic body 9 (such as a disk spring) presses the ring gate electrode 7 to the gate electrode 2a together with the external gate terminal 8 via an annular insulator 10.
Further shown is an insulator 11 for insulating the ring gate electrode 7 from the cathode distortion buffer disk 3 and the external cathode electrode 4, a first flange 12 secured to the external cathode electrode 4, a second flange 13 secured to the external anode electrode 6, and an insulating cylinder 14 made of ceramics or the like and which is divided into upper and lower parts. An outer periphery of the external gate terminal 8 protrudes out of a side of the insulating cylinder 14 and is hermetically secured to a divisional portion 14a by soldering. In addition, an end portion 15 secured to the insulating cylinder 14 by soldering is hermetically secured to the first and second flanges 12 and 13 by arc welding. Thus, the GCT 1 has a closed structure and the inside is filled with an inert gas.
Next, the operation of the GCT 1 will be explained. Current flows toward the external cathode electrode 4 from the external gate terminal 8 when the GCT 1 is turned on. A gradient of rise of the gate current at this time is generally set at 1000 A/xcexcs or more in operating the GCT 1 without a current limiting reactor and the turn-on spreading speed of the GCT 1 must be increased. While current flows toward the external gate terminal 8 from the external cathode electrode 4 when the GCT 1 is turned off, the current must be fed with the gradient of several thousands A/xcexcs to commutate a current equivalent to the main current of the GCT 1 to the gate in about 1 xcexcs to operate it without a snubber circuit. A contact resistance of a current feeding path from the external gate terminal 8 to the external cathode electrode 4 must be minimized to feed such a large current instantly.
While the cathode electrode 2b,the cathode distortion buffer disk 3 and the external cathode electrode 4 are pressed by a large force of several hundreds kg/cm2 from outside of the GCT 1, the gate electrode 2a, the ring gate electrode 7, and the external gate terminal 8 are pressed only by the elastic body 9. This is because the elastic body 9 is disposed at a peripheral part of the external cathode electrode 4. Thus, the pressure at a portion A, where the external gate terminal 8 contacts the ring gate electrode 7, is several kg/cm2 and a contact resistance sufficient to feed the above-discussed instantaneous large power cannot be obtained.
The above-constructed background GCT 1 also has the following problems.
First, there is a case in which the external gate terminal 8 causes a waviness in a circumferential direction at the contact portion A between an inner peripheral portion of the external gate terminal 8 and the ring gate electrode 7 due to a strain caused by a thermal residual stress from soldering the external gate terminal 8 and the divisional portion 14a of the insulating cylinder 14. In addition, because the external gate terminal 8 is only pressed by the elastic body 9, the pressure at the contact portion A is several kg/cm2 and the waviness can not be corrected. Therefore, the contact resistance of the contact portion A is greater than a desired contact resistance. That is, the contact resistance of the feeding path from the external gate terminal 8 to the external cathode electrode 4 is too large. Thus, the power feeding capability of the gate is inhibited, because the gradient of the inverse direction gate current is insufficient when the GCT 1 is turned off, for example.
Secondly, the abnormality of the contact caused by the waviness also results in a contact resistance which fluctuates within the plane of the ring-shaped external gate terminal 8. Thus, the power feeding capability of the gate partially drops, which causes an extreme drop in the turn-off capability of the GTC 1.
Thirdly, the GTC 1 abnormally generates heat by locally receiving electromagnetic induction from the magnetic field of an external circuit when operating at high frequencies, because iron or nickel alloy is used for the external gate terminal 8 to thereby solder with ceramics (which is the material of the insulating cylinder 14). This problem influences the characteristics of the semiconductor substrate 2.
Accordingly, one object of the present invention is to solve the above-noted and other problems.
Another object of the present invention is to provide a novel compression bonded type semiconductor device which decreases a contact resistance of a current feeding path from an external gate terminal to an external cathode electrode.
Yet another object of the present invention is to provide a novel compression bonded type semiconductor device which can suppress a fluctuation of contact resistance within the plane of the external gate terminal caused by waviness produced in the circumferential direction of the external gate terminal from occurring at a portion where the inner peripheral part of the external gate terminal contacts a ring gate electrode.
Still another object of the present invention is to provide a novel compression bonded type semiconductor device which prevents the external gate terminal from abnormally generating heat by locally receiving electromagnetic induction by the magnetic field of the external circuit when operating at a high frequency.
To achieve these and other objects, the present invention provides a novel gate electrode and a cathode electrode formed on a top surface of a semiconductor substrate, and an anode electrode formed on a back surface of the substrate. An external cathode electrode is disposed to be compression bondable to the cathode electrode and an external anode electrode is disposed to be compression bondable to the anode electrode. Also included is an insulating cylinder containing the semiconductor substrate, and an external gate terminal whose outer peripheral portion protrudes out of the side of the insulating cylinder and which is fixed to the insulating cylinder. The external gate terminal also has a protrusion formed at an inner peripheral portion and which abuts the gate electrode. In addition, the external gate terminal is pressed to the gate electrode by an elastic body. Thus, the external gate terminal directly contacts the gate electrode and a contact resistance which otherwise exists in the background art between the external gate terminal and the ring gate electrode is eliminated. Accordingly, it is possible to decrease the contact resistance of the feeding path from the external gate terminal to the external cathode electrode, and to improve the power feeding capability of the gate.
Further, a ring-shaped press-contact auxiliary block may also be provided between the protrusion of the external gate terminal and the elastic body. Thus, it is possible to reduce the fluctuation of a press-contact force at the portion where the external gate terminal contacts the gate electrode. This suppresses the fluctuation of the contact resistance within the plane of the external gate terminal from occurring, due to the waviness at the inner peripheral part of the external gate terminal by the strain caused by thermal residual stress in soldering the external gate terminal with the insulating cylinder.
Furthermore, the external gate terminal may include a first ring-shaped portion and the protrusion may include a second ring-shaped portion formed at an inner peripheral portion of the first ring-shaped portion. Thus, the external gate terminal directly contacts the gate electrode and a contact resistance is decreased.
In addition, the protrusion abutting the gate electrode may have a ring-shape. Thus, the press-contact force at the portion where the external gate terminal contacts the gate electrode may be increased by about several tens of times compared. with the background art. Thus, it is possible to obtain a contact resistance sufficient to feed a large power instantly, by correcting the waviness which otherwise occurs at the inner peripheral part of the external gate terminal due to the strain caused by the thermal residual stress in soldering the external gate terminal with the insulating cylinder.
Further, the external gate terminal may include a non-magnetic material, which suppresses the external gate terminal from abnormally generating heat by locally receiving electromagnetic induction by the magnetic field of an external circuit when operating at a high frequency.